newton's laws

newton's laws

Newton's laws in a nutshell

Mr. Anderson explains Newton's laws

(cut/paste link)

https://www.youtube.com/watch?v=PNTLDNxTMdg

Newton's 1st law: inertia or mass

Newton’s First Law (Inertia): In the absence of a net force, an object at rest stays at rest and an object in motion stays in motion at a constant speed in a straight line forever

This means: Things keep doing what they’re doing unless there’s a leftover force in some direction. If all forces balance, it keeps on keepin’ on.

This also means: When F=0, a=o (Follows from F=ma.) If acceleration is zero, it cannot be speeding up, slowing down, or changing directions. Its velocity is constant!!

Newton's 2nd law or F=ma

Newton’s Second Law (F=ma): 

A net force is a fancy name for the sum of forces

Net force = mass x acceleration.

or a = sum of all forces / mass of object

This means: If there is a leftover force, things will change. It will speed up, slow down, or change directions. That is, it will NOT have constant velocity. Recall that velocity includes direction!

Newton's 3rd law: action/reaction pairs

For every action there is an equal and opposite reaction.

This means: If two objects hit each other, they hit with the same force no matter what their masses or accelerations are. Always. These forces cannot cancel out even though they are the same amount and opposite directions because they aren’t on the same object. 

Example:1:  Earth pulls object down, object pulls Earth up

          2:  Horse pulls on apple cart, apple cart pulls on horse

         3.   Apple cart wheel pushes ground back, ground pushes apple cart forward

** key is to only look at the interaction between 2 objects **

Multiple Choice

An empty truck and a fully loaded truck are next to each other at a traffic light. When the light turns green, the lighter truck increases speed more quickly. Which of these best explains this situations

• Newton's first law
• Newton's second law
• Newton's third law
• Conservation of momentum

Multiple Choice

Which of these best describes why your weight (on Earth) would change on another planet?

• weight doesn’t change, no matter where you are
• different planets have different gravitational pulls
• In general, the smaller the planet, the greater weight
• dehydration effects on different planets change weight

Multiple Choice

To test Newton’s law of gravity, Ben and Jerry climbed the football stadium at school and dropped an egg from the very top of the bleachers. Their egg dropped data can be seen in the table According to this data, What conclusion can the boys make regarding Newton’s law of gravity?

• a)  No conclusion can be drawn from the data
• a)  The acceleration due to gravity is not constant
• a)  The acceleration due to gravity of 9.8 m/s2 is refuted
• a)  The acceleration due to gravity of 9.8 m/s2 is supported

Multiple Choice

An object will not have any inertia if it is __________?

• Accelerating
• Moving in a circle
• In space
• … Nonsense! All objects have inertia

Multiple Choice

A person in car  slides to the right when going through a very sharp left turn on the highway. 

• 1st Law
• 2nd Law
• 3rd Law

Multiple Choice

A person steps out of the boat and onto the dock.  As the person moves forward onto the dock, the boat moves backward.  Which statement best describes the backward motion of the boat as the person steps forward?

• For every action there is an equal and opposite reaction.
• Every mass exerts a force on every other mass.
• An object at rest tends to stay at rest.
• Friction opposes the motion of an object.

Multiple Choice

A magician pulls a tablecloth out from under dishes and glasses on a table without disturbing them.

• Newton's 1st Law
• Newton's 2nd Law
• Newton's 3rd Law
• None of them

Multiple Choice

A sled sliding on a flat, icy surface with a constant velocity is best described by

• Newton’s first law of motion for objects at rest.
• Newton’s first law of motion for objects in motion.
• Newton’s second law of motion.
• Newton’s third law of motion.

Multiple Choice

A crumpled piece of paper hits the ground before a flat sheet of paper because

• the acceleration of gravity is greater on the  crumpled paper.
• there is more air resistance against the flat paper.
• the crumpled paper is more massive
• the crumpled paper is less massive.

Multiple Choice

A cannonball with a mass of 0.5 kg is flying at an acceleration of 10 m/sec/sec. What is its force?

• 50 Newtons

• 5 Newtons

• 20 Newtons

• 9.5 Newtons

Multiple Choice

What is the acceleration of a 50 kg object pushed with a force of 500 newtons?

• 100 m/s²

• 25,000 m/s²

• 10 m/s²

• 25 m/s²

Multiple Choice

You push against a wall and the wall is pushing back on you.

• Newton's
  1st
  Law of Motion
• Newton's
  2nd
  Law of Motion
• Newton's
  3rd
  Law of Motion

Multiple Choice

An automobile you are riding in suddenly stops, but you continue to go forward.

• Newton's
  1st
  Law of Motion
• Newton's
  2nd
  Law of Motion
• Newton's
  3rd
  Law of Motion

Multiple Choice

When an unbalanced force acts on an object, the force ______________________.

• changes the motion of the object

• is cancelled by another force

• does not change the motion of an object

• is equal to the weight of the object

Multiple Choice

When two equal forces act in opposite directions on an object, they are called ______________________.

• frictional force

• balanced force

• centripetal force

• gravitational force

Multiple Choice

An archer pulls the bowstring back, then releases the string and the arrow flies forward. Pulling the string back is the...

• action force

• reaction force

• net force

• inertia

Multiple Choice

The combination of all the forces acting on an object is the...

• net force
• action force
• reaction force
• balance force

Multiple Choice

A force that opposes motion between a surface in contact with the atmosphere.

• air resistance
• gravity
• momentum
• terminal velocity

Multiple Choice

The force that opposes motion between two surfaces in contact with each other.

• inertia
• friction
• momentum
• gravity

Multiple Choice

The tendency of an object to resist changes in its motion is...

• inertia
• force
• acceleration
• velocity